1. Field of the Invention
The invention pertains to a vacuum chamber for flat substrates in which transport rollers provided for transporting the substrates are located above the bottom of the vacuum chamber and held at their two ends by one bearing each.
2. Discussion of the Prior Art
Vacuum chambers of this kind are being used, in particular, as lock chambers for flat glass coating systems, and are in general already known. In order to achieve the greatest possible process speed with installations of this kind, it is necessary to evacuate the vacuum chamber as quickly as possible. This can be achieved by using the smallest possible volume for the vacuum chamber and by using the greatest possible power for the pump which is used to evacuate the vacuum chamber.
At the present time, a drawn-in chamber cover, displacement elements between the transport rollers, and vacuum-tight transport rollers are known as means to reduce the chamber volume. It is possible by these means to reduce the chamber volume significantly. An additional, important reduction in the chamber volume would be possible if transport rollers with a smaller diameter could be used. But this design change is hindered by the fact that the transport rollers can only be supported by bearings at their ends and often must have a length of several meters. But, since they can only have a limited flexure to ensure a safe and direction-stable transport of the flat substrate, the large, free length necessarily requires a relatively large transport roller diameter, often more than 10 cm in today's equipment. An additional transport roller bearing in the middle of the vacuum chamber is not possible with the means available at the present time, because the chamber bottom acts like a membrane and moves by more than 1 mm during evacuation and ventilation.